IllustrisTNG Simulations Research Articles

Galaxy merger challenge: A comparison study between machine learning-based detection methods

Aims. Various galaxy merger detection methods have been applied to diverse datasets. However, it is difficult to understand how they compare. Our aim is to benchmark the relative performance of merger detection methods based on machine learning (ML). Methods. We explore six leading ML methods using three main datasets. The first dataset consists of mock observations from the IllustrisTNG simulations, which acts as the training data and allows us to quantify the performance metrics of the detection methods. The second dataset consists of mock observations from the Horizon-AGN simulations, introduced to evaluate the performance of classifiers trained on different, but comparable data to those employed for training. The third dataset is composed of real observations from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) survey. We also compare mergers and non-mergers detected by the different methods with a subset of HSC-SSP visually identified galaxies. Results. For the simplest binary classification task (i.e. mergers vs. non-mergers), all six methods perform reasonably well in the domain of the training data. At the lowest redshift explored 0.1 < ɀ < 0.3, precision and recall generally range between ~70% and 80%, both of which decrease with increasing ɀ as expected (by ~5% for precision and ~10% for recall at the highest ɀ explored 0.76 < ɀ < 1.0). When transferred to a different domain, the precision of all classifiers is only slightly reduced, but the recall is significantly worse (by ~20–40% depending on the method). Zoobot offers the best overall performance in terms of precision and F1 score. When applied to real HSC observations, different methods agree well with visual labels of clear mergers, but can differ by more than an order of magnitude in predicting the overall fraction of major mergers. For the more challenging multi-class classification task to distinguish between pre-mergers, ongoing-mergers, and post-mergers, none of the methods in their current set-ups offer good performance, which could be partly due to the limitations in resolution and the depth of the data. In particular, ongoing-mergers and post-mergers are much more difficult to classify than pre-mergers. With the advent of better quality data (e.g. from JWST and Euclid), it is of great importance to improve our ability to detect mergers and distinguish between merger stages.

The physical origin of the mass–size relation and its scatter for disk galaxies

Aims. In this study, we investigated the intricate interplay between internal (natural) and external (nurture) processes in shaping the scaling relationships between specific angular momentum (j⋆), stellar mass (M⋆), and the size of disk galaxies within the IllustrisTNG simulation. Methods. Using a kinematic decomposition of simulated galaxies, we focus on galaxies with tiny kinematically inferred stellar halos indicative of weak external influences. We examined the correlation between the mass, size, and angular momentum of galaxies by comparing simulations with observations and the theoretical predictions of the exponential hypothesis. Results. Galaxies with tiny stellar halos exhibit a large scatter in the j⋆ − M⋆ relation, which suggests that this scatter is inherently present in their initial conditions. Our analysis reveals that the disks of these galaxies adhere to the exponential hypothesis, resulting in a tight fiducial j⋆ − M⋆-scale length (size) relation that is qualitatively consistent with observations. The inherent scatter in j⋆ provides a robust explanation for the mass–size relation and its substantial variability. Notably, galaxies that are moderately influenced by external processes closely adhere to a scaling relation akin to that of galaxies with tiny stellar halos. This result underscores the dominant role of internal processes in shaping the overall j⋆ − M⋆ and mass–size relations, with external effects playing a relatively minor role in disk galaxies. Furthermore, the correlation between galaxy size and the virial radius of the dark matter halo exists but fails to provide strong evidence for a connection between galaxies and their parent dark matter halos.

Characterising galaxy clusters’ completeness function in Planck with hydrodynamical simulations

Galaxy cluster number counts are an important probe with which to constrain cosmological parameters. One of the main ingredients of the analysis, along with accurate estimates of cluster masses, is the selection function, and in particular the completeness associated with the cluster sample under consideration. Incorrectly characterising this function can lead to biases in cosmological constraints. In this work, we want to study the completeness of the Planck cluster catalogue, estimating the probability of cluster detection in a realistic setting using hydrodynamical simulations. In particular, we probe the case in which the cluster model assumed in the detection method differs from the shapes and profiles of true galaxy clusters. We created around 9000 images of the Sunyaev–Zel’dovich effect from galaxy clusters from the IllustrisTNG simulation, and used a Monte Carlo injection method to estimate the completeness function. We studied the impact of having different cluster pressure profiles and complex cluster morphologies on the detection process. We find that the cluster profile has a significant effect on completeness, with clusters with steeper profiles producing a higher completeness than ones with flatter profiles. We also show that cluster morphology has a small impact on completeness, finding that elliptical clusters have a slightly lower probability of detection with respect to spherically symmetric ones. Finally, we investigate the impact of a different completeness function on a cosmological analysis with cluster number counts, showing a shift in the constraints on Ωm and σ8 that lies in the same direction as the shift driven by the mass bias.

TESTING AN ENTROPY ESTIMATOR RELATED TO THE DYNAMICAL STATE OF GALAXY CLUSTERS

We propose the entropy estimator HZ, calculated from global dynamical parameters, in an attempt to capture the degree of evolution of galaxy systems. We assume that the observed (spatial and velocity) distributions of member galaxies in these systems evolve over time towards states of higher dynamical relaxation (higher entropy), becoming more random and homogeneous in virial equilibrium. Thus, the HZ-entropy should correspond to the gravitacional assembly state of the systems. This was probed in a sample of 70 well sampled clusters in the Local Universe whose gravitational assembly state, classified from optical and X-ray analysis of substructures, shows clear statistical correlation with HZ. This estimator was also tested on a sample of clusters (halos) from the IllustrisTNG simulations, obtaining results in agreement with the observational ones.

Merger-tree-based Galaxy Matching: A Comparative Study across Different Resolutions

We introduce a novel halo/galaxy matching technique between two cosmological simulations with different resolutions, which utilizes the positions and masses of halos along their subhalo merger tree. With this tool, we conduct a study of resolution biases through the galaxy-by-galaxy inspection of a pair of simulations that have the same simulation configuration but different mass resolutions, utilizing a suite of IllustrisTNG simulations to assess the impact on galaxy properties. We find that, with the subgrid physics model calibrated for TNG100-1, subhalos in TNG100-1 (high resolution) have ≲0.5 dex higher stellar masses than their counterparts in the TNG100-2 (low resolution). It is also discovered that the subhalos with M gas ∼ 108.5 M ⊙ in TNG100-1 have ∼0.5 dex higher gas mass than those in TNG100-2. The mass profiles of the subhalos reveal that the dark matter masses of subhalos in TNG100-2 converge well with those from TNG100-1, except within 4 kpc of the resolution limit. The differences in stellar mass and hot gas mass are most pronounced in the central region. We exploit machine learning to build a correction mapping for the physical quantities of subhalos from low- to high-resolution simulations (TNG300-1 and TNG100-1), which enables us to find an efficient way to compile a high-resolution galaxy catalog even from a low-resolution simulation. Our tools can easily be applied to other large cosmological simulations, testing and mitigating the resolution biases of their numerical codes and subgrid physics models.

Velocity Dispersions of Quiescent Galaxies in IllustrisTNG

We examine the central stellar velocity dispersion of subhalos based on IllustrisTNG cosmological hydrodynamic simulations. The central velocity dispersion is a fundamental observable that links galaxies with their dark matter subhalos. We carefully explore simulated stellar velocity dispersions derived with different definitions to assess possible systematics. We explore the impact of variation in the identification of member stellar particles, the viewing axes, the velocity dispersion computation technique, and simulation resolution. None of these issues impact the velocity dispersion significantly; any systematic uncertainties are smaller than the random error. We examine the stellar mass–velocity dispersion relation as an observational test of the simulations. At fixed stellar mass, the observed velocity dispersions significantly exceed the simulation results. This discrepancy is an interesting benchmark for the IllustrisTNG simulations because the simulations are not explicitly tuned to match this relation. We demonstrate that the stellar velocity dispersion provides measures of the dark matter velocity dispersion and the dark matter subhalo mass.

Stellar metallicity of galaxies: new insight on the formation and evolution of low surface brightness galaxies in the IllustrisTNG simulation

ABSTRACT In this work, we investigate the stellar metallicities of low surface brightness galaxies (LSBGs) and normal high surface brightness galaxies (HSBGs) in the IllustrisTNG100-1 simulation. LSBGs and HSBGs are classified as galaxies with mean central surface brightness $\mu _{\rm r} \gt 22.0 $ and $\mu _{\rm r} \lt 22.0\rm \ mag\ arcsec^{-2}$, respectively. Our findings indicate that both LSBGs and HSBGs exhibit similar number distributions of stellar metallicities at high redshifts (z > 1.5). However, at low redshifts (z < 1.5), a clear bimodal distribution of stellar metallicities in galaxies emerges, with LSBGs tending to be more metal-poor than HSBGs. The lower metallicity of LSBGs compared to HSBGs is mostly attributed to the pronounced gradient in the radial distribution of stellar metallicities. The bimodality of stellar metallicity is not attributed to colour distinctions but rather to the slower metal enrichment in LSBGs compared to HSBGs. This suggests that the mechanisms driving metal enrichment in LSBGs differ from those in HSBGs.

Interacting galaxies in the IllustrisTNG simulations – VI: Reconstructed orbits, close encounters, and mergers

ABSTRACT Cosmological simulations have been used to study interacting galaxies as a function of galaxy pair separation, enabling comparisons with observational studies of galaxy pairs. The study of interacting galaxies as a function of time (i.e. merger stage) has mostly been limited to high-resolution merger simulations, due to the poor time sampling available in cosmological simulations. Building on an earlier study of galaxy pairs in the IllustrisTNG cosmological simulations, we reconstruct the orbits of galaxy pairs involving massive galaxies (M* > 1010 M⊙) at redshifts of 0 ≤ z < 1, using a novel kinematic interpolation scheme to model the orbits in between the IllustrisTNG snapshots (which are separated by 162 Myr, on average). We assess the accuracy of these interpolations using a pre-existing suite of merger simulations, and find that kinematic interpolations provide a remarkable improvement in accuracy compared with interpolations that use only radial separations or 3D positions. We find that nearly 90 per cent of the closest pairs (r < 25 kpc) have had a pericentre encounter within the past Gyr. Many of these close pairs are found on rapidly shrinking orbits, and roughly 85 per cent of these pairs will merge within 1 Gyr. However, approximately 3 per cent of these close pairs appear to be flyby systems that will never merge. These reconstructed orbits will be used in future studies to investigate how and when galaxy properties change during close encounters and mergers between galaxies in IllustrisTNG.

Searching for cold gas traced by MgII quasar absorbers in massive X-ray-selected galaxy clusters

Almost 50<!PCT!> of galaxies in the local Universe are in clusters or groups coexisting with both hot and cold gas components. In the present study, we observationally probed the cold-gas content of X-ray-selected massive galaxy clusters with spectroscopic redshift measured from the SDSS/SPIDERS survey. This paper focuses on the most massive structures: galaxy clusters with a mean mass of M$_ 500c $ M$_ odot We used a large number of background quasar optical spectra from SDSS DR16 to probe the diffuse T$=$10$^4$K gas in their intracluster medium. We first analysed a sample of spectra with known MgII absorbers, and then blindly stacked about 16\,000 archival spectra at the redshifts of the foreground galaxy clusters. We tentatively ($3.7 significance) detect MgII in the clusters with an equivalent width EW(MgII lambda 2796) of 0.056pm 0.015 corresponding to a column density of log N(MgII)/cm$^ We tested our methodology by generating 22\,000 mock SDSS spectra with MgII absorbers from Illustris-TNG50 cosmological magnetohydrodynamical simulations, combining photo-ionisation modelling and ray tracing. We also performed bootstrapping stacking at different cluster redshifts and stacked quasar spectra with no intervening clusters in the line of sight to measure the significance of our detection. These results are in line with the findings of recent, similar observational studies but challenge predictions from Illustris-TNG simulations. Together, our findings indicate that large amounts of cold gas may be found in the most massive structures of the Universe.

Interacting galaxies in the IllustrisTNG simulations – VII: the connection between the most luminous active galactic nuclei and galaxy interactions

ABSTRACT We investigate the connection between the most luminous active galactic nuclei (AGN), galaxy pairs, and post-mergers in the IllustrisTNG simulation. We select galaxy pairs and post-mergers with a mass ratio between 1:10 < μ < 1:1 and a redshift between 0 < z < 1. We compare the incidence of luminous AGN in pairs with matched non-pair controls, finding that AGN with luminosity Lbol > 1044 erg s−1 occur in ∼26 per cent of paired galaxies with a companion within 20 kpc, compared with ∼14 per cent in controls (a fractional excess of ∼2). The enhancement of AGN in galaxy pairs is luminosity dependent, with the highest excess (a factor of ∼6 ± 2 at the closest separations) for AGN with Lbol > 1045 erg s−1. Additionally, pairs exhibit a modest yet statistically significant excess of luminous AGN up to ∼150 kpc in separation. For pairs which merge between 0 < z < 1, AGN fractions are elevated between 1.5 Gyr before and after coalescence, with the highest excess closest to coalescence. Our results indicate that pre-coalescence interactions drive excesses of luminous AGN, but that luminous AGN in galaxy pairs are not ubiquitous. Finally, we investigate what fraction of AGN can be associated with an interaction (either having a companion within 100 kpc or a merger within the last 500 Myr). For AGN with Lbol > 1045 erg s−1, ∼55 per cent are interacting, compared with a 30 per cent interaction fraction in AGN with 1044 < Lbol < 1044.5 erg s−1. Our results support a picture in which interactions play a dominant role in (but are not the sole cause of) triggering the most luminous AGN.

Improving the descendant relationship of cluster galaxies at z < 1

AbstractIn this work, we study how to improve well‐known techniques for detecting progenitors/descendants of galaxies, such as the NDpredict program, when applied to galaxies in clusters. The improvement of this particular method is based on the use of the red sequence of galaxies in those environments. Objects close to the red sequence in the color and magnitude diagram are more likely to belong to the cluster. This defines a probability scale which is then combined with the one generated by NDpredict. This procedure is optimized for the study of galaxies in clusters over different epochs. Our main result is that, for a sample composed of clusters, with masses greater than , selected from the IllustrisTNG simulations (namely, the TNG100 runs). In of the cases (i.e., systems), we obtain better performance with the red sequence method in comparison to the original NDpredict, and the average gain obtained is in the identification of descendants for this sample of cluster galaxies.

Analysis of Star Formation Main Sequences based on IllustrisTNG Simulations

As a matter of fact, N body simulations are widely used in cosmology and astrophysics. Thanks to the rapid development of computer resources, it is available to carry out galaxy simulations including magnetic evolution, for example, the project of IllustrisTNG and THESAN. In this case, based on the data collected from IllustrisTNG API, investigations into the star formation main sequence (SFMS) of dark matter (DM) halos are carried out by querying the accomplished simulation tasks. To be specific, multiple linear relation among the star formation rate (SFR) of DM halos, the stellar mass of DM halos and cosmological red shift are discovered. According to the analysis, a polynomial relation between the SFR and the stellar mass of DM halos is revealed, in which the coefficients are related to the redshift. Overall, these results shed light on guiding further exploration of star and galaxy formation based on analysis of the simulation results.

Mock Observations: Formation and Evolution of Diffuse Light in Galaxy Groups and Clusters in the IllustrisTNG Simulations

In this paper, by analyzing mock images from the IllustrisTNG100-1 simulation, we examine the properties of diffuse light and compare them to those of central and satellite galaxies. Our findings suggest that the majority of the diffuse light originates from satellites. This claim is supported by the similarity between the age and metallicity distributions of the diffuse light and those of the satellites. Notably, the color distribution of the diffuse light gradually evolves to resemble that of the centrals at lower redshifts, suggesting a coevolution or passive process. The radial profiles of the diffuse light reveal distinct trends, with the inner regions displaying a relatively flat distribution and the outer regions showing a descending pattern. This finding suggests that the formation of the diffuse light is influenced by both major mergers and stellar tidal stripping. Moreover, strong correlations are found between the stellar mass of the diffuse light and the overall stellar mass of the satellites, as well as between the stellar mass of the diffuse light and the number of satellites within groups or clusters. These relationships can be described by power-law and logarithmic functions. Overall, the diffuse light components predominantly originate from satellites with intermediate ages and metallicities. These satellites typically fall within the stellar mass range and the color range −1 < [g − r]0.1 < 0. As the redshift decreases, the growth of the diffuse light is primarily influenced by the redder satellites, while the most massive and reddest satellites have minimal roles in its growth.

Jellyfish galaxies with the IllustrisTNG simulations – citizen-science results towards large distances, low-mass hosts, and high redshifts

ABSTRACT We present the ‘Cosmological Jellyfish’ project – a citizen-science classification program to identify jellyfish (JF) galaxies within the IllustrisTNG cosmological simulations. JF are satellite galaxies that exhibit long trailing gas features – ‘tails’ – extending from their stellar body. Their distinctive morphology arises due to ram-pressure stripping (RPS) as they move through the background gaseous medium. Using the TNG50 and TNG100 simulations, we construct a sample of $\sim 80\, 000$ satellite galaxies spanning an unprecedented range of stellar masses, $10^{8.3}{-}10^{12.3}\, \mathrm{M_\odot }$, and host masses, $M_\mathrm{200,c}=10^{10.4}{-}10^{14.6}\, \mathrm{M_\odot }$ back to z = 2. Based on this sample, $\sim 90\, 000$ galaxy images were presented to volunteers in the citizen-science Zooniverse platform, who were asked to determine whether the galaxy image resembles a JF. Based on volunteer votes, each galaxy received a score determining if it is a JF or not. This paper describes the project, the inspected satellite sample, the methodology, and the classification process that resulted in a data set of 5307 visually identified JF galaxies. We find that JF is common in nearly all group- and cluster-sized systems, with the JF fraction increasing with host mass and decreasing with satellite stellar mass. We highlight JF galaxies in three relatively unexplored regimes: low-mass hosts of $M_\mathrm{200,c}\sim 10^{11.5}{-}10^{13}\, \mathrm{M_\odot }$, radial positions within hosts exceeding the virial radius R200, c, and at high redshift up to z = 2. The full data set of our JF scores is publicly available and can be used to select and study JF galaxies in the IllustrisTNG simulations.

Can the low-redshift Lyman alpha forest constrain AGN feedback models?

ABSTRACT We investigate the potential of low-redshift Lyman alpha (Lyα) forest for constraining active galactic nuclei (AGNs) feedback models by analysing the Illustris and IllustrisTNG simulation at z = 0.1. These simulations are ideal for studying the impact of AGN feedback on the intergalactic medium (IGM) as they share initial conditions with significant differences in the feedback prescriptions. Both simulations reveal that the IGM is significantly impacted by AGN feedback. Specifically, feedback is stronger in Illustris and results in reducing cool baryon fraction to 23 per cent relative to 39 per cent in IllustrisTNG. However, when comparing various statistics of Lyα forest such as 2D and marginalized distributions of Doppler widths and H i column density, line density, and flux power spectrum with real data, we find that most of these statistics are largely insensitive to the differences in feedback models. This lack of sensitivity arises because of the fundamental degeneracy between the fraction of cool baryons and the H i photoionization rate (ΓHI) as their product determines the optical depth of the Lyα forest. Since the ΓHI cannot be precisely predicted from first principles, it needs to be treated as a nuisance parameter adjusted to match the observed Lyα line density. After adjusting ΓHI, the distinctions in the considered statistics essentially fade away. Only the Lyα flux power spectrum at small spatial scales exhibits potentially observable differences, although this may be specific to the relatively extreme feedback model employed in Illustris. Without independent constraints on either ΓHI or cool baryon fraction, constraining AGN feedback with low-redshift Lyα forest will be very challenging.

Tilted Dark Halos Are Common and Long-lived, and Can Warp Galactic Disks

In the Lambda cold dark matter paradigm, the dark halo governs the gravitational potential within which a galaxy can form and evolve. In this Letter we show that the present-day inner (r < 50 kpc) dark halo can be significantly misaligned with the stellar disk. To this end, we use the TNG50 run from the cosmological magnetohydrodynamic IllustrisTNG simulation suite. Such “tilted” dark halos can arise from a variety of processes including major mergers, massive flybys, or interactions with satellite companions. Furthermore, we show that tilted dark halos (1) are well traced by tilted stellar halos, (2) can maintain their tilt for >5 Gyr in isolated evolution, and (3) can generate warps in the outer disks that are stable over many Gyr. A tilted dark halo holds clues to important events in the formation history of a galaxy, and could help explain the abundance of warped disks in galaxy observations, including the Milky Way.

Emission-line properties of IllustrisTNG galaxies: from local diagnostic diagrams to high-redshift predictions for JWST

ABSTRACT We compute synthetic, rest-frame optical and ultraviolet (UV) emission-line properties of galaxy populations at redshifts from z ≈ 0 to = 8 in a full cosmological framework. We achieve this by coupling, in post-processing, the cosmological IllustrisTNG simulations with new-generation nebular-emission models, accounting for line emission from young stars, post-asymptotic giant branch (PAGB) stars, accreting black holes (BHs) and, for the first time, fast radiative shocks. The optical emission-line properties of simulated galaxies dominated by different ionizing sources in our models are largely consistent with those expected from classical diagnostic diagrams and reflect the observed increase in [O iii]/Hβ at fixed [N ii]/Hα and the evolution of the Hα, [O iii]λ5007, and [O ii] λ3727 luminosity functions from z ≈ 0 to ∼ 2. At higher redshift, we find that the emission-line galaxy population is dominated by star-forming and active galaxies, with negligible fractions of shock- and PAGB-dominated galaxies. We highlight 10 UV-diagnostic diagrams able to robustly identify the dominant ionizing sources in high-redshift galaxies. We also compute the evolution of several optical- and UV-line-luminosity functions from z = 4 to 7, and the number of galaxies expected to be detectable per field of view in deep, medium-resolution spectroscopic observations with the NIRSpec instrument on board the JWST. We find that 2-h-long exposures are sufficient to achieve unbiased censuses of Hα and [O iii]λ5007 emitters, while at least 5 h are required for Hβ, and even 10 h will detect only progressively smaller fractions of [O ii] λ3727, O iii] λ1663, C iii] λ1908, C iv λ1550, [N ii]λ6584, Si iii] λ1888, and He ii λ1640 emitters, especially in the presence of dust.

High-redshift metallicity calibrations for JWST spectra: insights from line emission in cosmological simulations

ABSTRACT Optical emission-line ratios are traditionally used to estimate gas metallicities from observed galaxy spectra. While such estimators have been calibrated primarily at low redshift, they are commonly used to interpret observations of high-redshift galaxies, where their applicability may be questioned. We use comprehensive emission-line catalogues of galaxies from the IllustrisTNG simulation including ionization by stars, active galactic nuclei, and shocks to reassess the calibrations of both optical and ultraviolet metallicity estimators at redshifts $0\lesssim z \lesssim 8$. For present-day galaxies, the predicted optical-line calibrations are consistent with previously published ones, while we find different ultraviolet-line ratios, such as He ii λ1640/C iii] λ1908, can provide powerful metallicity diagnostics. At fixed metallicity, most emission-line ratios are predicted to strongly increase or decrease with redshift (with the notable exception of N2O2 = [N ii]λ6584/[O ii] λ3727), primarily because of a change in ionization parameter. The predicted dependence of R3 = [O iii]λ5007/H β and R23 = ([O ii] λ3727 + [O iii]λ5007)/H β, and to a slightly lesser extent R2 = [O ii] λ3727/H β and O32 = [O iii]λ5007/[O ii] λ3727, on O abundance for galaxies at z = 4–8 agrees remarkably well with Te-based measurements in 14 galaxies observed with JWST. This success motivates us to provide new calibrations of optical and ultraviolet metallicity estimators specifically designed for galaxies at z &amp;gt; 4, to guide interpretations of future, high-redshift spectroscopic surveys. We further demonstrate that applying classical z = 0 calibrations to high-redshift galaxies can bias oxygen abundance estimates downward by up to 1 dex, leading to the inference of stronger evolution of the mass–metallicity relation than is actually occurring.

Figure Rotation of IllustrisTNG Halos

We use the TNG50 and TNG50 dark matter (DM)-only simulations from the IllustrisTNG simulation suite to conduct an updated survey of halo figure rotation in the presence of baryons. We develop a novel methodology to detect coherent figure rotation about an arbitrary axis and for arbitrary durations, and we apply it to a catalog of 1577 DM halos from the DM-only run and 1396 DM halos from the DM+baryons (DM+B) run that are free of major mergers. Figure rotation was detected in 94% of DM-only halos and 82% of the DM+B halos. The pattern speeds of rotations lasting ≳1h −1 Gyr were log-normally distributed with medians of 0.25 h km s−1 kpc−1 for DM-only in agreement with past results, but 14% higher at 0.29 h km s−1 kpc−1 in the DM+B halos. We find that rotation axes are typically aligned with the halo minor or major axis in 57% of DM-only halos and in 62% of DM+B halos. The remaining rotation axes were not strongly aligned with any principal axis but typically lie in the plane containing the halo minor and major axes. Longer-lived rotations showed greater alignment with the halo minor axis in both simulations. Our results show that, in the presence of baryons, figure rotation is marginally less common, shorter-lived, faster, and better aligned with the minor axis than in DM-only halos. This updated understanding will be consequential for future efforts to constrain figure rotation in the Milky Way dark halo using the morphology and kinematics of tidal streams.

CASCO: Cosmological and AStrophysical parameters from Cosmological simulations and Observations – I. Constraining physical processes in local star-forming galaxies

ABSTRACT We compare the structural properties and dark matter content of star-forming galaxies taken from the Cosmology and Astrophysics with MachinE Learning Simulations (camels) cosmological simulations to the observed trends derived from the SPARC sample in the stellar mass range $[10^{9}, 10^{11}]\, \textrm {M}_{\odot }$, to provide constraints on the value of cosmological and astrophysical (supernova- and active galactic nucleus-related) parameters. We consider the size–, internal DM fraction–, internal DM mass–, and total–stellar mass relations for all the 1065 simulations, all having different cosmological and astrophysical parameters, from the IllustrisTNG, SIMBA, and ASTRID suites of camels, and search for the parameters that minimize the χ2 with respect to the observations. For the IllustrisTNG suite, we find the following constraints for the cosmological parameters: $\Omega _{\textrm {m}} = 0.27_{-0.05}^{+0.01}$, $\sigma _{8} = 0.83_{-0.11}^{+0.08}$, and $S_{8} = 0.78_{-0.09}^{+0.03}$, which are consistent within 1σ with the results from the 9-yr WMAP observations. SN feedback-related astrophysical parameters, which describe the departure of outflow wind energy per unit star formation rate and wind velocity from the reference IllustrisTNG simulations, assume the following values: $A_{\textrm {SN1}} = 0.48_{-0.16}^{+0.25}$ and $A_{\textrm {SN2}} = 1.21_{-0.34}^{+0.03}$, respectively. Therefore, simulations with a lower value of outflow wind energy per unit star formation rate with respect to the reference illustrisTNG simulation better reproduce the observations. Variation of active galactic nucleus feedback parameters, on the other hand, shows negligible effects on the scaling relation trends in the mass range probed. Simulations based on SIMBA and ASTRID suites predict central dark matter masses substantially larger than those observed in real galaxies, which can be reconciled with observations only by requiring values of Ωm inconsistent with cosmological constraints for SIMBA, or simulations characterized by unrealistic galaxy mass distributions for ASTRID.